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Mailbox Formats
===============
Mailbox formats supported by Dovecot:
+-----------------------------+---------------+-------------------+-------------+
| *Name* | *Tag* | *Description* |
+-----------------------------+---------------+-------------------+-------------+
| <mbox> | 'mbox' | Traditional UNIX |
| [MailboxFormat.mbox.txt] | | mailbox format. |
| | | Users' INBOX |
| | | mboxes are |
| | | commonly stored in|
| | | '/var/spool/mail' |
| | | or '/var/mail' |
| | | directory. Single |
| | | file contains |
| | | multiple messages.|
+-----------------------------+---------------+-------------------+-------------+
| <Maildir> | 'maildir' | One file contains |
| [MailboxFormat.Maildir.txt] | | one message. A |
| | | reliable choice |
| | | since files are |
| | | never modified and|
| | | all operations are|
| | | atomic. The |
| | | top-level |
| | | 'Maildir' |
| | | directory contains|
| | | the 'Maildir/cur',|
| | | 'Maildir/new' and |
| | | 'Maildir/tmp' |
| | | subdirectories. |
+-----------------------------+---------------+-------------------+-------------+
| <dbox> | 'sdbox' | *single-dbox*, one| Dovecot's |
| [MailboxFormat.dbox.txt] | | message per file | own high |
| | | | performance |
| | | | mailbox |
| | | | format. |
| | | | Messages are|
| | | | stored in |
| | | | one or more |
| | | | files, each |
| | | | containing |
| | | | one or more |
| | | | messages. |
+-----------------------------+---------------+-------------------+-------------+
| 'mdbox' | *multi-dbox*, |
| | multiple |
| | messages per |
| | file |
+-----------------------------+---------------+-------------------+-------------+
| 'dbox' | deprecated |
| | alias for |
| | 'sdbox' |
+-----------------------------+---------------+-------------------+-------------+
| <Cydir> | 'cydir' | Dovecot's own |
| [MailboxFormat.Cydir.txt] | | simple and high |
| | | performance |
| | | Cyrus-like mailbox|
| | | format. It should |
| | | be mostly used for|
| | | testing and |
| | | benchmarking only.|
+-----------------------------+---------------+-------------------+-------------+
| <imapc> | 'imapc' | Use remote IMAP |
| [MailboxFormat.imapc.txt] | | server as mail |
| | | storage. |
+-----------------------------+---------------+-------------------+-------------+
| <pop3c> | 'pop3c' | Use remote POP3 |
| [MailboxFormat.pop3c.txt] | | server as mail |
| | | storage. |
+-----------------------------+---------------+-------------------+-------------+
The *Tag* column indicates the tag which is used at the beginning of a <mailbox
location specification> [MailLocation.txt].
Mailbox formats *not* supported by Dovecot:
+-------------------------------+---------------------------------------------+
| *Name* | *Description* |
+-------------------------------+---------------------------------------------+
| <mbx> [MailboxFormat.mbx.txt] | UW-IMAP's old high performance mailbox |
| | format. One file contains all the mailboxes,|
| | so expunges may still be slow. |
+-------------------------------+---------------------------------------------+
| <mix> [MailboxFormat.mix.txt] | UW-IMAP's new (2006) high performance |
| | mailbox format. Similar to multi-dbox. |
+-------------------------------+---------------------------------------------+
| <mailstore> | A format created by Exim. |
| [MailboxFormat.mailstore.txt] | |
+-------------------------------+---------------------------------------------+
| <MH> [MailboxFormat.MH.txt] | One file contains one message. Sort order of|
| | the folder determines the message ID and |
| | name. Actively used by projects such as |
| | MH-E, NMH, exmh. Experimentally supported |
| | by UW-IMAP |
| | [https://www.washington.edu/imap/]. |
+-------------------------------+---------------------------------------------+
| <MMDF> [MailboxFormat.MMDF.txt]| Similar to mbox, but instead of From-line |
| | separators it uses four '^A' characters |
+-------------------------------+---------------------------------------------+
| <Cyrus> | One file contains one message, plus there |
| [MailboxFormat.Cyrus.txt] | are a couple of index/cache files. Commonly |
| | referred to as being maildir-like, although |
| | they have only a single thing in common. |
+-------------------------------+---------------------------------------------+
Adding support for new formats for Dovecot isn't very difficult, although it
can be time consuming. Dovecot exposes a nice and simple API which needs to be
implemented. Use Cydir format as an example.
Software Support
----------------
+-------------------------------+-----------------------------+-------------------------------------+--------------------------------------+--------------------------+-----------------------------+-------------------------------------+--------------------------+------------------------------+------------------------------------------+
| *Format/Software* | *Dovecot | *UW-IMAP | *Courier-IMAP | *Exim | *Postfix | *PINE | *mutt | *procmail | *maildrop |
| | [https://www.dovecot.org/]* | [https://www.washington.edu/imap/]* | [https://www.courier-mta.org/imap/]* | [https://www.exim.org/]* | [https://www.postfix.org/]* | [https://www.washington.edu/pine/]* | [https://www.mutt.org/]* | [https://www.procmail.org/]* | [https://www.courier-mta.org/maildrop/]* |
+-------------------------------+-----------------------------+-------------------------------------+--------------------------------------+--------------------------+-----------------------------+-------------------------------------+--------------------------+------------------------------+------------------------------------------+
| <mbox> [MailboxFormat.mbox.txt]| Yes | Yes | No | Yes | Yes | Yes | Yes | Yes | Yes |
+-------------------------------+-----------------------------+-------------------------------------+--------------------------------------+--------------------------+-----------------------------+-------------------------------------+--------------------------+------------------------------+------------------------------------------+
| <mbx> [MailboxFormat.mbx.txt] | No | Yes | No | Yes | No | Yes | No | No | No |
+-------------------------------+-----------------------------+-------------------------------------+--------------------------------------+--------------------------+-----------------------------+-------------------------------------+--------------------------+------------------------------+------------------------------------------+
| <maildir> | Yes | No | Yes | Yes | Yes | No | Yes | Yes (3.22) | Yes |
| [MailboxFormat.Maildir.txt] | | | | | | | | | |
+-------------------------------+-----------------------------+-------------------------------------+--------------------------------------+--------------------------+-----------------------------+-------------------------------------+--------------------------+------------------------------+------------------------------------------+
| <mailstore> | No | No | No | Yes | No | No | No | No | No |
| [MailboxFormat.mailstore.txt] | | | | | | | | | |
+-------------------------------+-----------------------------+-------------------------------------+--------------------------------------+--------------------------+-----------------------------+-------------------------------------+--------------------------+------------------------------+------------------------------------------+
| <dbox> [MailboxFormat.dbox.txt]| Yes | No | No | No | No | No | No | No | No |
+-------------------------------+-----------------------------+-------------------------------------+--------------------------------------+--------------------------+-----------------------------+-------------------------------------+--------------------------+------------------------------+------------------------------------------+
| <MH> [MailboxFormat.MH.txt] | No | Yes | No | No | No | Yes | Yes | Yes | No |
+-------------------------------+-----------------------------+-------------------------------------+--------------------------------------+--------------------------+-----------------------------+-------------------------------------+--------------------------+------------------------------+------------------------------------------+
Conversion Between Mailbox Formats
----------------------------------
See <Migration.MailFormat.txt>.
References
----------
* Mutt mailbox formats: https://rucus.ru.ac.za/docs/mutt/manual58.html
* Article on mailbox formats:
https://www.livejournal.com/users/rfunk/1571.html
* Mbox and maildir comparison:
https://www.linuxmail.info/mbox-maildir-mail-storage-formats/
(This file was created from the wiki on 2019-06-19 12:42)
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